[aurays]

Hi there,

I was wondering how coordinating conjunctions work in sentences with commas.

Something like:

I finished my homework, but I should have finished earlier.

I know you can use but, or, and for after a comma. Are there any other coordinating conjunctions?

Also, how does it work with the conjunction so? I many times saw it with a comma before and in other cases without a comma. What would be the right use of it?

Thank you!

[susan53]

There's no rule for commas with co-ordinators when they join clauses. You could write eg in an email :
Sorry John. I was going to come to the meeting but I have the flu.
or
Sorry John. I was going to come to the meeting, but I have the flu.
Generally though, commas would be more usual if what came either or after was particularly long and complex, in order to give the reader a pause:
John and his family had wanted to visit the museums in Rome on their holiday, but they all caught the flu and spent the whole week in bed.
Notice the comma before but after the long statement but not before and after just a short one.

The only "pure " single words co-ordinators are and, but and or, though there are also correlative co-ordinators like either/or, not only /but also made up of two parts. The tests for the single word co-ordinators are that :

1. They can join not simply clauses but also other items of the same word class - eg two nouns - fish and chips; two adverbs slowly but surely; two verbs - sink or swim

2. They can never precede each other.

3. They can precede subordinating conjunctions : He was tired and although he wanted to see the film, he decided to go to bed.

4. They can only occur between the two items they join, and never in any other position.

So is technically an adverb not a co-ordinating conjunction. Notice that it doesn't meet condition (2) above. Eg : he was tired and so he decided to go to bed. is fine. [/i] But it is often used like one in more informal writing where a comma reflects the sort of pause a speaker might make : He was tired, so he decided to go to bed. But I'd avoid this in formal writing such as academic essays, job applications etc.

[aurays]

Thank you susan53 for the detailed explanation! It helped me a lot to understand better how to use these coordinating conjunctions

I did a little more research and came across 'yet' but I didn't see how I could use it. Is it also considered a coordinating conjunction?

[susan53]

Yes, yet is usually classed as a co-ordinating conjunction, but is an odd one. It doesn't meet the rules for either subordinating conjunctions or sentence adverbials, so can't be classed with them, but on the other hand doesn't meet all the conditions for co-ordinating conjunctions either.

a) Why can't it be a subordinating conjunction?

Subordinating conjunctions, like although, are part of the clause they introduce. If the clauses swap position the subordinating conjunction moves:
He failed the exam, although he had studied really hard.
Although he had studied really hard, he failed the exam.

Co-ordinators like but, and and or can't do this. They have to stay in the middle of the two ideas. Yet is the same

He'd studied really hard, but he failed the exam.
He failed the exam, but he'd studied really hard.
He'd studied really hard, yet he failed the exam.
He failed the exam, yet he'd studied really hard.

b) Why can't it be a sentence adverb?

Sentence adverbs, like however, also come with the second idea, but they can be, and often are, separated from the rest of the clause by commas, and are flexible in position :

He studied very hard. However, he still failed the exam.
He studied very hard. He still, however, failed the exam.
He studied very hard. He still failed the exam, however.

You can't do that with co-ordinating conjunctions - they must come at the beginning of the second idea, whether they are in the same sentence or start a new one.

He had studied really hard. But/Yet he still failed the exam.

c) So why is "yet" different to the "pure" co-ordinating conjunctions??

So far yet has behaved identically to but. But there is one rule which but and and or follow that yet breaks - they can't combine with each other. I can, for example, combine a sentence adverb with a co-ordinating conjunction:

He studied really hard but still failed the exam, however.

and I can do the same with yet :

He studied really hard, but/and yet he failed the exam.

but I can't do it with but :

*He studied really hard and but he failed the exam.

[aurays]

Thanks susan53 for writing the answer! I always had this thing where I was not really sure how to classify yet, but now I see that it makes a lot of sense once you know how it all works.